The Merced river flows peacefully through the Yosemite Valley.
You can rent rafts at Camp Curry Village (but don’t plan on staying there unless you can cope with high-density low-privacy Butlins) with the put-in a short walk down to the river. Once on the water you can paddle or float gently down the river, admiring the crowd-free views of the valley as you go. If floating becomes too much, you can just beach the raft on a beach
to explore cool-off with a swim (or a splash) and watch the wildlife.
(H ‘stalked’ the deer to get the pic above. Good one!)
All-in-all a proper float .Note: This post was updated on 2020-11-15 to fix broken links